Touch screen is the device of inputting the signal in accordance with the calculation of the coordinates when a particular section on the screen is directly/indirectly touched with hand or tool, etc.
For the large size touch screen among conventional touch screen technologies, the infrared method which recognizes the coordinates within the touch screen by using the infrared sensor is mainly used, and the representative system of this infrared method is the opto-matrix system which is the method of recognizing the touched section by arranging several units of light emitting elements and light receiving elements and conducting simultaneous or sequential transmission and reception so that a grid structure is constituted at the upper section of screen and touching the screen with finger or the item which can intercept the light and calculating the coordinates of the point where the reception of light is intercepted.
This kind of infrared touch screen is applied to the touch screen which is relatively large, and has the advantages that it can possess excellent performance based on high reliability and can be embodied with relatively low cost, therefore, the prospect of market activation is highly probable in the future and it is expected to be the representative model of the touch screen of next generation.
When considering the infrared touch screen from the viewpoint of recent market demand, the size of display panel is becoming larger, however, the size of bezel is in the trend of becoming thinner and smaller on the contrary, therefore, all the related structures constituting the touch screen are in the trend of slimming down. For the touch panel with the structure of thin bezel, the demands for installing not only at indoor environment where the influence of sunlight is not existed, but also at outdoors or at the inside of building where large amount of sunlight is coming in (similar outdoors) are in the trend of increasing gradually, and the utilization of large size touch screen is also being increased.
However, large size touch screen has the problems of generating the malfunction of touch or dropping of the operation velocity since the noise is increased at the SNR of infrared transmission light signal because the maximum detection value of infrared reception element is abnormally raised as large amount of direct and indirect influence is received by the interference wavelength radiated from sunlight (to be referred to as “external light” hereafter), and hence, the detection value (signal) of infrared reception unit by the touch of user becomes conspicuously lowered compared to the maximum detection value which was abnormally raised by the external light.
The basic cause for these problems is that the effect of the infrared filter used for the infrared touch screen with thin bezel structure is not sufficient enough for its intercepting function (removing rate) of external light, and this is because of the fact that if the size of touch screen is increased, the interference of external light becomes larger.